SSDs often use more than two values. The nice thing about binary is it is the most resistant to fluctuation. In the real world, if 1.2V is high and 0V is low, you are going to see many voltages other than the perfect values especially when transitioning. With binary you can say something like "If > 0.2V, 1, otherwise 0" whereas the more states you add, the more bands you have to create. "If < 0.2V, 0. If >= 0.2 V and < 0.6 V, 1. If >= 0.6 V, 2". The bins will keep getting smaller the more digits you allow.